1. Field of the Invention
The present invention relates to a back check for a piano which locks a hammer after it has struck a string to prevent the hammer from rebounding.
2. Description of the Prior Art
A conventional action having a back check is disclosed, for example, in Laid-open Japanese Patent Application No. 2003-36073. FIG. 1 illustrates an action 60 when a key 2 is released. The action 60, which may be for use with an acoustic grand piano, comprises a wippen 4 carried on a rear portion of the key 2 for pivotal movement about a rear end (left end in FIG. 1) thereof; a repetition lever 5 pivotably attached to the wippen 4; a jack 6; and a repetition spring 7 for urging the repetition lever 5 and jack 6 in a return direction (counter-clockwise direction in FIG. 1).
A key weight, not shown, is attached to a front portion of the key 2, such that a touch feeling is adjusted for the key 2 by balancing the key weight with the action 60 and the like. The repetition lever 5 is formed with a jack guide hole 5c extending vertically through a front portion thereof, and a hammer 3 is carried near the jack guide hole 5c through a shank roller 8.
The hammer 3 comprises a hammer shank 14 extending in a longitudinal direction and having a shank roller 8 attached thereto; a hammer head 15 attached at the leading end of the hammer shank 14; and the like. The hammer shank 14 has a proximal end pivotably attached to a hammer flange 16. The hammer head 15, which is made of a wood material, comprises a hammer wood 35 extending in the vertical direction; and a hammer felt 34 wound around a top portion of the hammer wood 35 for striking a string S extending above the hammer head 15.
The jack 6, which is pivotably attached to a fulcrum 4b in an upper end portion of the wippen 4, is generally formed in an L-shape, and has the upper end inserted in a jack guide hole 5c of the repetition lever 5 for movement along the jack guide hole 5c. A jack button screw 11 is screwed through the jack 6 in the longitudinal direction in such a manner that the jack button screw 11 can be moved front and rear in order to adjust the angular position of the jack 6.
A jack button 12 is formed integrally with the leading end of the jack button screw 11. The jack button 12 is attached to the jack 6 with the jack button screw 11 being screwed into one end surface thereof at the center. The jack button 12 has the other end surface in contact with a spoon 13 of the wippen 4.
On the top surface of a rear end portion of the key 2, a back check 40 is attached through a seat plate 2a and a back check wire 41 with a slight spacing defined between the back check 40 and a tail 35a of the hammer wood 35. The back check 40 comprises a back check body 42; and a cushion material 43 adhered from the front surface to an upper portion of the back surface of the back check body 42.
As the key 2 is depressed from the key released state, the wippen 4 is pushed up to make a pivotal movement, causing the repetition lever 5 and jack 6 to move up together with the wippen 4. Associated with these movements, the repetition lever 5 first slides the shank roller 8 and simultaneously pushes up the hammer 3 through the shank roller 8, causing the hammer 3 to make a pivotal movement. Next, the repetition lever 5 is brought into engagement with the drop screw 9, causing the upper end of the jack 6 to push up the hammer 3 through the shank roller 8. Subsequently, at the time the hammer 3 has pivotally moved until immediately before it strikes the string S stretched above, the front end of the jack 6 is brought into engagement with the regulating button 10 to make a pivotal movement, and moves away from the shank roller 8. Consequently, the hammer 3 is released from the coupling with the action 60 and key 2, and strikes the string S in a freely pivotable way.
The hammer 3, which has struck the string S, pivotally moves in the return direction by a reaction of striking the string S. In this event, the key 2 remaining depressed causes the back check 40 in the rear end portion of the key 2 to be positioned at a level higher than when the key 2 is in the key released state. The tail 35a of the hammer 3 in the pivotal movement for returning collides with the back check 40 in the foregoing state. Since the cushion material 43 is adhered on the back check 40, the hammer 3, which has come into contact with the back check 40, is locked and stopped at that position without making a rebound.
Subsequently, at a timing at which the key 2 is released and returned to some extent, the repetition lever 5 begins to initiate its action, wherein the repetition lever 5 pivotally moves with a spring force of the repetition spring 7 to return in the counter-clockwise direction, thereby sliding and simultaneously pushing up the shank roller 8. This permits the jack 6 to pivotally move with the spring force of the repetition spring 7 to return in the counter-clockwise direction, and the jack button 12 to come into contact with the stopper 13, thereby returning to an original angular position. In this way, at the time the jack 6 returns to the original angular position, the hammer 3 had already been stopped as mentioned above, so that the hammer 3 can strike the string S the next time even if the key 2 has not been completely returned, thus permitting the hammer 3 to successively strike the same string S. In this way, the same key 2 can be rapidly beaten in succession as is the case with playing trill.
On the other hand, a back check structured in the following manner is also known in the past. As illustrated in FIG. 2, a back check 50 comprises a back check body 51; an under felt 52; and a leather 53 having cushioning properties. The back check body 51 is formed with a flatly cut felt adhering surface 51a in an upper half of a front surface of the back check body 51. The under felt 52 is adhered to the felt adhering surface 51a. The under felt 52 is shaved with a sandpaper or the like after the adhesion for shaping such that its upper portion is thicker than its lower end portion. The leather 53 in turn is adhered from the lower end of the front surface to an upper portion of the back surface of the back check 50 to cover the under felt 52. Thus, the surface of the leather 53 on the front side presents a smooth curve, with a slight recess substantially at the center in the vertical direction in conformity to the shape of the under felt 52. Thud, during a pivotal movement of the hammer 3 associated with key depression from the key released state, the tail 35a of the hammer 3 pivotally moves along the curved surface of the leather 53 to avoid a contact with the back check 50 without fail. Also, immediately after the hammer 3 has struck the string S, the tail 35a of the hammer 3 which makes a pivotal movement for returning by the reaction of striking the string S is locked by the small recess in the leather 53 to more effectively mitigate a shock when the hammer 3 collides with the back check 50, thereby making it possible to stop the hammer 3 with more certainty.
However, the conventional back check for a piano described above has the following problems. Specifically, for providing the leather 53 with the curved surface, the under felt 52 must be shaped with a sandpaper or the like after it has been adhered to the back check body 51, causing a corresponding increase in the manufacturing cost.
The back check is attached to a rear end portion of the key 2 at a position away from the fulcrum of the key 2 in a grand piano, whereas the back check is attached at a position away from the center of the pivotal movement of the wippen in an upright piano. Thus, in either type of piano, the weight of the back check relatively significantly affects a static load which determines a touch feeling of the key 2, so that a certain amount of key weight must be attached to a front portion of the key 2 in order to ensure a proper static load. As such, the amount of the key weight cannot be reduced, leading to a failure in saving the manufacturing cost.